The present invention relates to a new and improved construction of a material web drier which is of the type containing a device for controlling the gas flow or stream of a drying medium as a function of the actual condition of the material web which is to be dried.
Generally speaking, the material web drier of the invention is of the type comprising surfaces arranged in coacting relationship with respect to the material web and provided with blow-out or discharge openings, especially constructed in the form of air infeed lines structured as nozzle casings or boxes having openings directed towards the material web and serving for the discharge of the drying medium, there being provided intermediate spaces or interstices formed by the nozzle casings arranged in spaced relationship from one another in order to enable drawing or sucking-off of the drying medium.
Such general type of prior art material web drier has been disclosed in U.S. Pat. No. 3,995,375, granted Dec. 7, 1976. Also in U.S. Pat. No. 3,930,319, granted Jan. 6, 1976 there is disclosed a drying apparatus for drying a traveling web, particularly a paper web, wherein a hot air delivery structure is mounted in coacting relationship with a steam heated cylinder to direct jets of hot air against the traveling web supported upon the cylinder. Also known in this technology is a drying hood, as disclosed in British Pat. No. 953,248, published Mar. 25, 1964, wherein such drying hood fits around a drying cylinder of a papermaking machine for the purpose of drying the fabricated paper web. A still further construction of drying apparatus is disclosed in Austrian Pat. No. 233,941, granted June 10, 1964.
As is well known, it is the purpose of a material web drier to render possible an effective delivery of the drying medium to the material web and to again draw-off such drying medium. During this drying process moisture is delivered by the material web to the drying medium and then the drying medium laden with the picked-up moisture is withdrawn.
It is well known when processing web or sheet-like materials, such as paper webs, to remove the moisture from such materials with the aid of a drying medium. To this end, the drying medium, during such time as the material web is continuously moved upon a suitable conveying device, is blown onto the material web by means of discharge or outflow channels and again withdrawn by means of further channels. There have been used for this purpose so-called nozzle casings or discharge surfaces and by means of discharge openings for the drying medium, which are directed onto the material web, the drying medium is blown onto such material web. By means of special outflow or withdrawal openings the drying medium which is enriched with the moisture removed from the treated material is again sucked-off. Particularly significant in this regard is the aforementioned U.S. Pat. No. 3,995,375.
As a general rule, the discharge openings are structured as bores, but however they can also be formed as slots which can be designed in the most different variations. The purpose of such discharge openings, whether they are slots, bores or otherwise, is to always have the drying medium impinge as uniformly as possible over the material web, in order to realize a uniform drying characteristic of the treated material.
It is also known to the art, especially from Austrian Pat. No. 308,524, granted Oct. 15, 1972, to provide a drying apparatus with discharge or blow-out openings for the drying medium such that the drying medium does not only linearly impact against the material web, rather strikes the material web at an inclination through a certain angle. To prevent resucking-up of the drying medium directly at the preceding discharge opening, it is also known to use a discharge location as an air curtain.
Also there is known a method by means of which there can be controlled the moisture characteristic or profile of paper during its fabrication. Hence, at a number of locations of the material web there is measured the moisture content. With the aid of control signals, formed as a function of the thus measured moisture content, two of such control signals are employed for controlling the lateral bearing of the material web at the pressure roll in order to reduce changes in the moisture profile. A third control signal is used for the uniform change in the moisture content of the material web. By means of this method for controlling the moisture profile during paper fabrication, it is intended to insure that certain residual moisture, which is formed at a number of regions of the material web more intensely than at other regions, is compensated.
Yet, these measures are associated with the drawback that there are required complicated devices, in order to obtain a change in the profile of the moisture content. The problem really is not attacked at its root, since the drying medium is uniformly applied to the material web, and thus, there cannot be taken into account any influence upon possibly formed moisture zones.